Whenever I get a message or an email or a comment regarding
unsuccessful bridge circuits, it’s usually along the lines of no output being
observed, the MOSFETs getting hot, or everything just getting damaged or
blowing up. When I was in the preliminary stages of bridge design, I also had
repeated failures. I had circuits blowing up. I had circuits just not working,
no matter what. I’ve written on my blog about one such experience of mine. You
can read it here:http://tahmidmc.blogspot.com/2012/10/magic-of-knowledge.html

In this article, I’ll talk about the first things you should
do if your attempts at designing a bridge circuit have gone up in smoke or if
you’re designing a bridge circuit and want to ensure everything has been done
properly.

Another thing I should mention is that, in almost all cases
of people asking for help, the bridge driver (the high-low side driver) has
been the IR2110 (or similar, such as IR2112, IR2113, etc). Remember that most
bootstrap-based high-low side drivers function in pretty much the same way. So,
I’ll talk about the driver in general here. I had, however, written a tutorial regarding the IR2110. So, if you're interested regarding that check out:

The first thing to do is to check everything over and over again. I know it's cliched and it's probably the most repeated thing you’ve heard, but it's also the least
appreciated or followed. One missing
connection (or an extra one too, eg a short) could be the cause of all the mayhem.

1) Firstly, check the connection of the bridge itself. Ensure
that all the MOSFETs are connected correctly.

2) Check the power connections to the drivers. Make sure that
the supply voltage is within acceptable bounds. Ensure that you have small
decoupling/bypass capacitors (0.1µF ceramic capacitors) along with larger
filter capacitors (for example, 10µF electrolytic capacitors). Use the 0.1µF
capacitors across all power lines.

3) Check the connections to the drivers, ie the driving signals
coming from the PWM controller, microcontroller, etc. Make sure that the
signals for the high-side MOSFET and the low-side MOSFET of one leg of the bridge don’t
overlap. If, in any way, both the high-side and low-side MOSFET turn on
simultaneously, this will be a dead short-circuit. Expect some ka-boom and
smoke. Use an oscilloscope to ensure that the signals don’t overlap.

4) Check the bootstrap circuitry. Make sure you’re using the
proper diodes – ultrafast diodes when required. Make sure your bootstrap
capacitor is large enough, but not too large. As I had previously mentioned,
there is a simple guideline I follow. For low frequencies and high on-times,
use large capacitors. 47µF to 68µF could be used for 50Hz/60Hz, for
example. For higher frequencies, eg 30kHz, use smaller capacitances, eg 10µF.

5) Check the connections from the drivers to the bridge
MOSFETs. Ensure that you’ve placed a series gate resistor between each driver
output and MOSFET gate. Ensure that you’ve connected the virtual ground
(obtained using the bootstrap capacitor; for example, this is the pin 5 – VS –
of the IR2110) to the corresponding high-side MOSFET source. Check that you’ve
connected the high-side output of the driver to the high-side MOSFET gate and
that you’ve connected the low-side output of the driver to the low-side MOSFET
gate.

6) Check that you have placed a gate to source resistor between
the gate and source of each MOSFET. I always use a 1kΩ resistor. If you have a
number of MOSFETs in parallel, have a gate to source resistor for each MOSFET.
Choose the resistance such that the combined resistance is about 1kΩ.
For example, if you have three MOSFETs in parallel, for each MOSFET use a 3.3kΩ
resistor. This will give a combined resistance of 1.1kΩ (you can use 3kΩ
resistors to get a combined resistance of 1kΩ).

Read here about one of my experiences where I damaged loads of drivers and MOSFETs all due to the lack of gate-to-source resistors:

7) Ensure that you have used the same ground for the drivers
and the controller generating the drive signals (microcontroller, PWM
controller, etc) and the bridge. Most (all that I’ve used) bootstrap-based
high-low side drivers are non-isolated drivers. The input and output stage are
not isolated from each other. Hence, the driver must share the same ground with
both the input stage (which is the microcontroller, PWM controller, etc) and
the output stage (which is the bridge that is being driven).

If you have a faulty bridge design and are making changes to
it, replacing some components to try again, I suggest you get rid of everything
and construct the circuit again using no parts from the old circuit. A faulty
MOSFET can damage the driver and vice versa. A faulty driver may damage other
parts and so there may be other damaged parts on your circuit that you don’t
even know are damaged.

If you follow these tips/hints, you should be able to
successfully design bridge drive circuits with no problem. Following these
tips/hints will also help you solve problems in any existing bridge drive
circuit.

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About Me

I am Syed Tahmid Mahbub, from Dhaka, Bangladesh, born on August 1, 1994.
Electronics is my passion and from class V, I have been learning electronics. I learnt and worked mostly on SMPS, power electronics, microcontrollers and integration of microcontrollers with SMPS and power electronics. I've used PIC and AVR microcontrollers - PIC 10F, 12F, 16F, 18F, 24F, dsPIC 30F, 33F, PIC32, ATmega and ATtiny, integrating them with various SMPS and power electronics circuits.
I have completed my Bachelor's degree from Cornell University (Class of 2017) in Ithaca, New York, USA, majoring in Electrical and Computer Engineering (ECE).
I am a member of the forum www.edaboard.com, where I am an "Advanced Member Level 5" (the highest level attainable) and also the forum allaboutcircuits.com, where I am a "Senior Member". I post to help solve electronics-related problems of engineers and engineering students from all over the world.
I love watching and playing cricket and football (soccer), and listening to music.
I am now a hardware engineer at Apple in Silicon Valley, California, USA.